Yarn temperature control



Sept. 19, 1967 R. D. CARR 3,342,975

YARN TEMPERATURE CONTROL Filed July 23, 1964 NVENTORS: v R0 T D.CARR

FRED W. LENOIR R -t a M United States Patent 3,342,975 YARN TEMPERATURE CONTROL Robert D. Carr and Fred W. Le Noir, Hopewell, Va., as-

signors to Allied Chemical Corporation, New York, N.Y., a corporation of New York Filed July 23, 1964, Ser. No. 384,753 3 Claims. (Cl. 219-388) ABSTRACT OF THE DISCLGSURE A process of regulating the temperature of a continuously running multifilament yarn by passin the yarn in continuous running contact With a glass capsule mounted in a heat insulator and containing a thermistor. In particular the capsule is mounted to pass radially through a plastic annulus just downstream from a heating zone through which the running yarn passes; and the supporting annulus is positioned so that the running yarn makes light tangential contact with the convex surface of the supporting annulus and passes over the protruding surface of the glass capsule, thereby exchanging heat with the thermistor.

Control apparatus responsive to the electrical condition of the thermistor is disclosed involving an electric bridge circuit including the thermistor and a pair of resistors on opposite sides of the bridge, each resistor being adjacent to a heater which heaters are switched olf and on in alternation as the changing balance across the bridge actuates a relay. The relay also turns the power to the heating zone off and on. A proportionating effect is obtained by the heating of the resistors, which heating accelerates the required response of the relay for correcting temperature deviations in the yarn heating zone.

This invention relates to process of controlling the flow of heat between a continuously running multifilament yarn and its surroundings; in particular to a process for maintaining such yarn at prescribed temperatures, e.g. a constant temperature, during a continuous treatment thereof at elevated temperature.

The invention further relates to apparatus which is particularly suitable for carrying out the above process and which can also be used in other instances where it is desired to regulate the flow of heat to and from a given zone.

It has been recognized in the art of treating yarnsespecially synthetic yarns of organic thermoplastic material such as linear polyamides; linear polyesters; polyvinyl chloride; polyvinylidene chloride; polyacrylonitrile; polyolefins such as polyethylene, polypropylene; cellulose acetate, etc.that when heat is employed in treating such yarn, maintenance of uniform yarn temperature is very important if uniform physical properties and dyeability of the resulting yarns are to be obtained.

Generally in the art, it has been attempted to maintain adequate temperature uniformity during heat treatments by sensing and correspondingly controlling the temperature of the heated zone. However when yarns are run continuously through a heat treatment and particularly when run at commercial speeds such as 150 feet per minute and higher, more particularly at speeds above 500 feet per minute, it has been very diflicult to maintain the desired temperature uniformity. Problems arise not only through non-uniformity of temperature in the heated zone itself, but also through non-uniform transfer of heat to the yarn arising through variation in application of yarn finish, changes in yarn moisture content, irregularities in any heated surface over which the yarn is moving, etc.

There has accordingly been a need for simple and effective means to control directly and continuously the Patented Sept. 19, 1967 temperature of the running yarn itself. Such means have, however, been lacking in the art.

Direct contact between a temperature sensing means and the running yarn Would appear called for to obtain the necessary quick response and'to minimize effects of the surroundings on the temperature being sensed. If there is to be direct contact between the temperature sensing means and the running yarn, the area of contact must be very small for several reasons. The sensing means contacting the running yarn must not damage the yarn nor provide a point at which heat is withdrawn in any but a highly regular manner from the yarn. Moreover the sensing means itself must be small so that its heat capacity will be low, allowing it to respond to small heat flows. At the same time its sensitivity must be very high in order to provide quick and close control of yarn temperature. Frictional effects due to the contact with the yarn should be minimal and must be controllable to a substantially constant level so as to avoid a false temperature reading due to friction. An instrument for direct contact with the yarn must also be rugged enough to withstand breakage in use. Finally, the instrument used must be affected only by changes in the yarn temperatures and not by fluctuations in the temperatures or other conditions such as humidity, etc. of the surroundings.

All of these requirements are well met by the present invention. The process of our invention comprises passing a multifilament yarn in continuous running contact with a smooth, abrasion resistant surface in heat exchange relationship with a body that changes its electrical resistance when its temperature is changed; said body'being characterized by temperature coefficient of resistance of at least about 1% per degree centigrade at C.; said body being insulated from temperature fluctuations in its surroundings other than the temperature changes in said yarn; and passing electrical current through said body and through a control circuit operatively connected there to and to process control means adapted to control the heat flow between said yarn and its surroundings responsive to changes in the electrical resistance of said body.

Our apparatus comprises a temperature sensitive resistance element that changes its electrical resistance when its temperature changes, positioned to respond to temperature changes in the given zone; an electrical bridge circuit having two branches, each branch having a pair of legs and each pair of legs having a junction between them; said temperature sensitive element being included in one leg; a pair of resistors which can be heated and change their resistances on heating, one in each of two adjoining legs of said bridge circuit, whereby the heating of each one resistor reinforces the effect upon balance across the bridge, due to variation in one sense of the temperature of the temperature sensitive element; connected across the junction of the legs of one branch and the junction of the legs of the other branch, a relay circuit adapted to operate in response to voltage changes across said junctions; switching elements operated by said relay circuit which in each of their switching positions, cause heating of only one of said resistors-which can be heated; and means operated in one sense in one position of said switching elements and in the reverse sense in the other position of said switching elements to cause respectively supply and withdrawal of heat to the zone in which the temperature is to be controlled, compensatively to changes in resistance of said temperature sensitive resistance element; the switching elements which cause the resistors to be alternately heated being coordinated with the switching elements for supply and withdrawal of heat to the controlled zone, in the sense that the supply of heat to said zone will be on simultaneously with the supply of heat to the one resistor which, when heated, reinforces the effect on the balance across the bridge due to a cold condition of the temperature sensitive element.

In a preferred form of our invention the temperature sensitive body which changes its electrical resistance in response to temperature changes is a semiconductor made of a sintered mixture of metallic oxides, and encased in a smooth surfaced, abrasion resistant material such as glass having thermal conductivity of at least about calorie/sec. cm. C. In this embodiment the glass forms a capsule around the semiconductor, of width not more than 5 times the width of the semiconductor and not more than about A", whereby said capsule has adequate heat conductivity and adequately low heat capacity for quick response to temperature changes in yarn contacting the capsule surface.

In order to hold the tempearture sensitive capsule in a fixed position where its friction with the running yarn will be constant, and at the same time to protect the capsule from breakage and to insulate the surface of the capsule except that surface which is in contact with the yarn, the capsule in a preferred embodiment of our invention is set in an insulating material having thermal 'conductivity not more than half of that of the material 'encasing the semiconductor, and not more than about '10" calorie/sec. cm. C. Organic plastics are generally twice. as high as that of the insulating support, the semiconductor within the capsule changes temperature only in response to temperature changes in the yarn passing thereover, even when its area of contact with the yarn is smaller than its areaof contact with the support. The

"sensitivity of the semiconductor, of at least about 1% change in resistance per degree centigrade at 100 C.,

' coupled with the small size of the capsule and its resulting low heat capacity, provide sensitive temperature response. In a preferred form of the invention, the insulating material supporting the semiconductor capsule has a convex surface from which the capsule protrudes radially, and the running yarn is brought into contact with the capsule and into light tangential contact with the convex supporting surface. In this way the yarn is caused to substantially completely surround the exposed portion of the capsule while making only light contact with the capsule support. The capsule thus supported is desirably positioned just downstream, say about one inch, from the heat treating zone through which the yarn is passing, so that the emerging yarn when it contacts the capsule will be at substantially the temperature it reaches in the heat treating zone. The emerging yarn passes immediately into contact with the capsule, and any guides or the like are positioned downstream from the capsule so as to avoid flow of heat to or from the yarn after the heat treating zone and before the temeprature sensitive capsule.

The temperature sensitive capsule is incorporated in an electrical control circuit which is in turn operatively connected to process control means such as a switch for turning a heater in the heat treating zone on and off. This heater can be the sole heater in the zone or it can be a secondary heater used to provide only a small proportion of the total heat supplied to the yarn, whereby the inertia 1 of a large heating system can be avoided. Alternatively the control means can regulate conditions other than the heat supply in the heating zone, such as rate of air flow therethrough or rate of yarn speed therein, whereby to control the heat flow between the yarn and its surroundmgs.

The control circuit through which the temperature sensitive semiconductor influences the process control means can take a variety of forms. A preferred form which we have found to be very well suited for the purposes of this invention and other purposes is illustrated in the accompanying drawings and described in detail below.

In the drawings:

FIG. 1 is a perspective view showing one embodiment of a temperature sensing device according to the present invention;

FIG. 2 is an enlarged vertical section taken generally along line 22 of FIG. 1;

FIG. 3 is an enlarged fragmentary view of a portion of the device of FIG. 1;

FIG. 4 is an enlarged horizontal section taken generally along line 44 of FIG. 3; and

FIG. 5 is a circuit schematic illustration of a system which operates according to the present invention.

The temperature sensing device shown in FIG. 1 will be seen to comprise a generally annular support member 10, having an encapsulated temperature sensitive element 12 radially set therein and protruding from its peripheral surface. A pair of guide members 14 also protrude from the support member surface on either side of but circumferentially displaced from the temperature sensitive element 12. The support member 10 is formed of a rigid insulating material, such as plastic, so as to maintain the temperature sensitive element and guide members in proper positional relationship and provide thermal insulation. Materials such as nylon, phenol-formaldehyde resin and polyester resin have been found suitable for this purpose.

Referring now to FIG. 2, it will be seen that the support member 10 is provided with an internal cavity 16 within which the sensitive element 12 and the guide members 14 are mounted. The sensitive element 12 is embedded in the material of the support member 10; and is positioned so that a portion of its tip protrudes out through the peripheral surface of the support member.

The sensitive element in the present embodiment takes the form of a probe type thermistor, comprising a temperature sensitive core which is encapsulated .in glass. The temperature sensitive core is a semiconductor formed of a powdered metallic oxide which has been pressed and sintered together as a ceramic. Such cores may be formed of oxides of manganese, nickel, cobalt, copper, iron or uranium. In their sintered form these materials are characterized by a high negative temperature coefiicient connected into a sensing and control circuit to be described hereinafter. v

The guide members 14, as shown in FIGS. 2 and 3, are mounted within the support member 10 and extend outwardly through its peripheral surface at points circumferentially displaced from the protruding tip of the sensitive element 12. These guide members are bent to form a channel to guide a moving yarn 22 over the sensitive element 12. They should be very smooth so as not to snag on the material moving between them. The location of the guide members, as indicated, is downstream, in the direc tion of yarn movement from the temperature sensitive element 12. This insures that any variations in temperature of the yarn, which may take place as a result of its sliding over the guide members, will not cause an erroneous reading at the sensitive element.

The enlarged fragmentary view of FIG. 4 illustrates the manner in which the device achievesaccurate temperature indication of a rapidly moving strand of fibrous material. As shown in FIG. 4, the moving strand of yarn 22. whose temperature is to be measured, is guided over the protruding tip of the temperature sensitive element 12. In passing over the element, the yarn covers its protruding portion. Since the remainder of the sensitive element 12 is fully embedded within the thermally insulating material of the support member 10, only this protruding portion of its tip is affected by changes in temperature. Because of the annular configuration of the support member 10, and the tangential contact of the yarn therewith, only an exceedingly small portion of the yarn as it first contacts the sensing device will touch anything but the protruding tip of the sensitive element 12 so that the amount of heat lost to the sensing device is minimal. Consequently, no appreciable temperature distortion at the sensitive element is introduced as a result of heat'transfer between the device and the yarn.

The protruding tip of the temperature sensitive element may be varied in configuration so long as the tip brings the core material of the sensitive element into thermal communication with the yarn, and not with the other surroundings. The tip thus should not protrude an excessive distance above the surface of the support member otherwise too great a surface area of its thermally conductive casing will be exposed to the atmosphere, allowing appreciable heat loss thereto from the core material. On the other hand, if the protruding tip does not extend sufficiently above the surface of the support member, too great a surface area of the yarn will come into contact with the material of the support member and will produce undesired and temperature distorting friction and heat transfer effects. It has been found best to utilize a sensitive element with a protruding tip diameter between .014 and .04 inch for measuring yarns of from 15 to 400 denier and a tip diameter between .04 and 15 inch for yarn of from 500 to 15,000 denier; and where the tip of the temperature sensitive element is of generally hemispherical configuration( the height/width ratio of its protruding portion should be maintained somewhere between 0.2 and 0.8 in order to avoid the heat loss and thermal distortion problems mentioned; and at the same time to secure maximum accuracy and temperature sensitivity.

The yarn temperature control system of FIG. 5 includes an electrically controlled yarn heating device 30', a temperature sensing device 32 comprising a supporting and insulating annulus 10 (of FIGS. 14) in which is mounted, as shown in FIGS. 14, a glass-encased temperature sensitive element 12; a resistance bridge circuit 34; and a relay switching system 36.

The output wires 18 and of the sensing device'32 are shunted across a resistor 37 in one leg of the resistance bridge circuit 34, whereby resistance due to sensing device 32 is included in this leg, but only a low current will pass through sensing device 32 so as to avoid appreciable heating thereof by the current therethrough.

The bridge circuit 34 includes branches 48 and 50 connected together at common input junctions 52 and 54 across an AC power source 56. Branch 48 of the bridge circuit is made up of a pair of legs having respectively resistors 58 and 60 therein, and connected together at output junction 62. Branch 50 is made up of a second pair of legs 57, 59 connected together at output junction 64 and containing respectively resistors 37, 38 (variable), 82; and 61, 84. The relative values of the resistances in the four legs control the voltage across the output junctions 62 and 64.

The output junction 62 of the bridge circuit is connected to the grid of a first amplifier tube 66. The cathode of this tube is connected, via variable resistance 71, to output junction 64 of the bridge. The plate circuit of this tube is connected via a plate resistor 68 to a further power source 70. When the resistance values in the various legs of the bridge have a certain ratio representing imbalance,

the resulting voltage across the output junctions 62 and 6 64 allows the first amplifier tube 66 to conduct. This point can be adjusted by variable resistance 71. This conduction results in relatively low voltage on he plate of the tube.

The plate of tube 66 is coupled via condenser 69 to the grid of a second amplifier tube 72, this grid being grounded through resistor 73. This second amplifier tube 72 is connected as shown, with its cathode at ground potential. Its plate is at the potential developed by power source 70 in series with the actuating coil of relay 46. When the condition of balance of the bridge changes so that tube 66 no longer conducts, this allows an increase in voltage between grid and cathode of the second amplifier tube 72, causing current flow in tube 72. The relay becomes energized and moves its various switch contacts from the position shown in FIG. 5 to the alternative position, in which the yarn heater is turned on by contacts 42.

Switch contacts 74 are connected in each of their alternative positions to one of two electrical heater elements 76 and 78 located respectively in the adjoining legs 57 and 59 of branch 50 of the bridge circuit 34. It will be seen that as the relay switches these contacts 74, the heater elements 76 and 78 are alternately placed in circuit with a further power source 80. Thus when the relay 46 has its switch contacts in the position shown in FIG. 5, the first heater element 76 in the first leg 57 of the lower bridge circuit branch is in operation while the second heater element 78 in the remaining leg is disconnected; and when the relay 46 is energized to switch the contacts, this situation is reversed.

The electrical heater elements '76 and 78 are placed in close proximity to associated electrical resistors 82 and 84 whose value of resistance increases with increasing temperature. It will be observed that at any time, one of the resistors is being heated while the other is cooling.

The balance condition of the bridge depends on the value of the following ratio K between the resistances in the legs:

The heating of resistor 82 by heater 76 increases its resistance, R in the above formula, and therefore decreases the value of the ratio K. In time K thus reaches a point at which tube 66 no longer conducts, and current flows in tube 72 causing actuation of the relay and switching of its various contacts. This results in cooling resistor 82 and heating resistor 84, with eventual raising of the value of K to the point where the relay is deenergized again. Consequently there is provided a free running system which periodically causes the relay'46 to energize and switch its contacts, then to de-energize and reverse its contacts. The periodic switching action of the relay causes its contacts 42 to turn the yarn heating device periodically on and off at intervals corresponding to the switching rate of the relay.

Control of the yarn temperature is maintained by the variation in length of On vs. Off times for the yarn heatin device, which results as will next be explained from the variation of resistance of the temperature sensing device 32 as its temperature is changed, combined with the action of the heated resistors 82 and 84 upon the bridge circuit. For example when the yarn heater is off and the yarn temperature goes down, the electrical resistance of the temperature sensing device 32 goes up, enhancing the rate of decrease in resistance ratio K produced by the heating of resistor 82 in leg 57, to turn the yarn heater on. On the other hand when the yarn heater is on, high resistance of element 32 due to low yarn temperature tends to offset an increasing resistance in leg 59 due to heating of resistor 84 therein thus keeping the yarn heater turned on.

When the yarn temperature is constant, the yarn heater switches on and 01f at regular intervals in response to the alternate heating of the two resistors 82 and 84.

Accordingly when yarn temperature is dropping, the bridge circuit actuates the reversal of the relay more quickly in the phase of operation while the first heater element 76 is turned on than it does while the second heater element 78 is turned on. But the relay switch 42 turns yarn heating device 30 on, only when the second heater element 78 is on. As just explained, this heater 78 will stay on for increasingly longer durations during longer and during more rapid drops in yarn temperature, causing the yarn heater 30 likewise to stay on longer, the more the deviation of yarn temperature below the prescribed value. This relationship of yarn heater On to yarn heater Off times is of course reversed when yarn temperature begins to rise. The result is a proportionating action by which a longer corrective heating or cooling of yarn heater 30 is effected, the more the yarn temperature deviates from its prescribed value.

The variable resistor 38 allows adjusting the above formulated ratio, K, of the resistances to maintain the temperature desired; and variable resistor 71 allows ad justing the length of the On-Off cycle of the relay.

A visual indication of the running yarn temperature is easily obtained by providing an ammeter 86 placed in series with either of the two leads 18 and 20 to the sensing element 32. Alternatively a voltmeter 88, or other voltage responsive indicating device can be provided across the two leads.

Specific examples illustrative of use of our process and apparatus in the heat treatment of yarns are presented belOW.

EXAMPLE 1 Temperature sensitivity at difierent yarn speeds and tension A 3-pound bobbin of nylon 6 yarn of 3600 denier, 210 filament count and zero twist was exposed in an oven for 16 hours to equilibrate in temperature. The oven temperature was measured by thermocouples located at various points in the oven, their readings being averaged. The average oven temperature was thus determined to be 124.4 C.

The yarn was then withdrawn from the oven through an outlet aperture at various speeds and tensions, and was immediately, at about 1 inch from the outlet aperture brought into contact with a capsule containing a temperature sensitive semiconductor made from sintered metal oxides, which had resistance of 100,000 ohms at room temperature and (negative) temperature coefiicient of resistance of about 3% per C. at 100 C. The capsule containing the semiconductor was of glass and approximately hemispherical, with diameter of 2.5 mm. The diameter of the semiconductor was 1.075 mm. The capsule was set rigidly along the diameter of a phenolformaldehyde resin annulus, protruding above its surface to height of .750 mm. or 30% of the diameter of the capsule, as in FIG. 2 of the drawings. About /3 of the glass surface around the semiconductor was thus exposed to continuously contact the running yarn, the remaining surface of the capsule being insulated by the resin. The circuitry permitted a maximum of 0.8 milliamp current flow through the semiconductor at full scale deflection of a voltmeter across the leads to the semiconductor. A recording amrneter allowed determination of the temperature measured by the semiconductor.

At yarn speeds of 40 ft./min. 700 ft./rnin. and 1500 ft./min., the yarn temperature recorded was found to be 124.0 C. at each speed. This test demonstrated high accuracy of yarn temperature indication, independent of yarn speed; and showed there was no apperciable heat loss from the yarn between the outlet aperture and the capsule.

Running the yarn at constant speed of 700 ft./min.

and varying the tension of the yarn over wide limits demonstrated that the yarn temperature sensing device gave uniform and accurate temperature read-out at all tensions. The tensions tested were 2.0 grams (.0056 gram per denier), 20 grams total tension (.0056 gram per denier), and grams total tension (.028 gram per denier). The temperature recorded was a constant 124 C. at all tensions.

The yarn temperature sensing device of this example produces accurate temperature read-out independent of yarn tension, indicating that frictional forces developed between the yarn and the capsule surface are practically negligible under the conditions used.

EXAMPLE 2 Efiect of height of semiconductor probe upon temperature sensing The same apparatus and test procedure as that described for Example 1 was employed, except that the glass capsule containing the semiconductor was allowed to protrude above the surface of the supporting plastic annulus to a height of 2.5 millimeters, i.e. about the full diameter of the capsule proper. The yarn split on each side of the capsule, exposing the top of the capsule to the air. The average temperature recorded was 122 C. and was substantially constant. An inaccuracy of 2 C. in the determination of temperature of a running yarn would be a significant error in processing textile yarns. Accordingly although the sensing of temperature in this example had considerably better precision than :1 C., nevertheless this mode of operation may sometimes be less desirable than the more accurate method of Example 1.

EXAMPLE 3 Drawing 0 nylon-6 yarn and the efiect of precise control over fiber properties An apparatus as illustrated in FIGS. 1-5 of the drawings and above described in connection therewith, using the yarn temperature sensing device of Example 1, was used to control the temperature of a heater employed in a yarn drawing operation. Column 2 of the table below summarizes the results thus obtained.

In operations summarized in column 1 of the table below, the temperature of the heater was used, in conventional manner, to control the heat input to the heater. The yarn temperature exit the heater in both test operations was measured as in Example 1 above.

The yarn temperature exit the heater was controlled by the process an dapparatus of this invention within i1 C.; whereas the yarn temperature variation exit the heater using conventional means of control was i5 C.

The yarn supplied for these tests was 136 filament zero twist nylon-6 yarn, which was drawn in the drawing operation to 840 denier and was wound up with producers twist of about /2 turn per inch. Improved uniformity was evident in all of the yarn properties of the table, and in tensile modulus a higher value was also obtained, when using the process and apparatus of this invention versus the control.

9 EXAMPLE 4 The efiect of precise thermal control in the crimping and bulking of yarn vs. poor thermal control on fiber properties The temperature of yarn in a heating zone following a crimping operation was controlled by the method and apparatus of Example 3 above; and was compared as in Example 3 to the temperature of like yarn, controlled by conventional means from the heating zone temperature. The properties of the resulting crimped yarns were also compared, the results being as shown in the table below.

The yarn supplied in these tests was 1200 denier, 7O filament hot drawn nylon-6 yarn, the yarn treated in accordance wtih this invention having been processed in drawing and other preliminary heating steps with temperatures controlled in accordance with this invention; whereas the control yarn was processed using conventional temperature controls at all stages. Thus the variations in properties for the two yarns, summarized in the table below, are cumulative variations for the entire processing of the two yarns.

The variations in properties, developed when using conventional temperature control, accumulated to such an extent that differences in dyeing properties and other yarn properties were apparent in finished products made from the control yarn of this example; whereas like products, made from the yarn of this example processed in accordance with this invention, were highly uniform in appearance and properties. I

The speed of yarn travel used in this example was 700 feet per minute.

We claim:

1. Process of continuously regulating the flow of heat between a running multifilament yarn and its surroundings which comprises: passing said yarn in continuous running contact with a smooth, abrasion resistant surface in heat exchange relationship with a body that changes its electrical resistance when its temperature is changed; said body being characterized by temperature coefiicient of resistance of at least about 1% per degree centigrade at 100 C.; said body being insulated from temperature fluctuations in its surroundings other than the temperature changes in said yarn; and passing electrical current through said body and through a control circuit operatively connected thereto and to process control means adapted to control the heat flow between said yarn and its surroundings responsive to changes in the electrical resistance 'of said body; said yarn being of organic thermoplastic material; said body changing its electrical resistance when its temperature changes being a semiconductor made of a sintered mixture of metallic oxides; said surface in heat exchange relationship with said body having thermal conductivity of at least about 1O calorie/sec. cm. C., said body being encased in the material of said surface to form a capsule around said body of width not more than five times the width of said body and not wider than about A inch; said yarn being in continuous running contact with at least about /5 of the surface of said capsule; and substantially all of the remaining surface of said capsule, which is not in contact with the running yarn, being surrounded and rigidly supported by insulating material having thermal conductivity not more than half that of the material in TABLE Comments, Col. 1

Example 4 Comments, Col. 2

Very good uniformity of appearance.

Shrinkage, percent- Carpet Cover Needs Improvement.

Creep Back, percent.

Needs Improvement....

Crimp Level Uniformi Although the above sets forth and describes the best mode contemplated by us for carrying out our invention; many modifications can be made by one skilled in the art without departing from the scope of the invention. For example although it is convenient and highly satisfactory to position the temperature sensitive element directly in the running yarn by the means above described, such position is not always essential and the temperature sensitive element can, for example, be po sitioned beneath or within a heat conductive shoe or within a heat conductive guide or the like which is contacted by the running yarn.

As another alternative to the above specific embodiment of apparatus, from the above formula for critical resistance ratio K it will be appreciated that any one of the resistances in the numerator can be that of a resistor which is heated instead of resistor 84; and likewise any of the resistances in the denominator can be that of a resistor heated instead of resistor 82. Again, although the temperature sensitive element of the herein examples has a negative temperature coefficient of resistance, an element mm a positive coefiicient of at least about 1% per C. can be used. With that substitution in the circuit of FIG. 5, the position of switch 74 will be reversed to put heater 78 on with switch 42 open, so that resistors 82 and 84 will, when each is heated, reinforce the effect of the temperature sensitive element upon the balance across the bridge, to correct deviations from the prescribed temperature. Many like variations will be apparent.

which said body is encased, and not more than 10 calorie/sec. cm. C.

2. Process of claim 1 wherein the material in which said body is encased is glass, and the supporting and insulating material is an organic plastic.

3. Process of claim 1 wherein the suporting material has a convex surface and said capsule protrudes radially from said convex surface; wherein said capsule is positioned just downstream from a heating zone through which the running yarn passes; wherein the yarn coming from said heating zone passes immediately into contact with said capsule and makes light tangential contact with said convex surface supporting the capsule; and wherein said process control means operates in response to changes in electrical resistance of said body to vary, compensatively to said changes, the amount of heat supplied to said yarn heating zone.

References Cited UNITED STATES PATENTS 2,753,714 7/1956 Perkins et al. 73-362 2,933,708 4/1960 Elliot et a1. 338 28 3,013,785 12/1961 King 3448 X 3,117,361 1/1964 Crouzlet 28-62 3,183,718 5/1965 Schnedler 3448 X RICHARD M. WOOD, Primary Examiner;

R. F. STAUBLY, Assistant Examiner. 

1. PROCESS OF CONTINUOUSLY REGULATING THE FLOW OF HEAT BETWEEN A RUNNING MULTIFILAMENT YARN AND ITS SURROUNDINGS WHICH COMPRISES: PASSING SAID YARN IN CONTINUOUS RUNNING CONTACT WITH A SMOOTH, ABRASION RESISTANT SURFACE IN HEAT EXCHANGE RELATIONSHIP WITH A BODY THAT CHANGES ITS ELECTRICAL RESISTANCE WHEN ITS TEMPERATURE IS CHANGED; SAID BODY BEING CHARACTERIZED BY TEMPERATURE COEFFICIENT OF RESISTANCE OF AT LEAST ABOUT 1% PER DEGREE CENTRIGRADE AT 100* C.; SAID BODY BEING INSULATED FROM TEMPERATURE FLUCTUATIONS IN ITS SURROUNDINGS OTHER THAN THE TEMPERATURE CHANGES IN SAID YARN; AND PASSING ELECTRICAL CURRENT THROUGH SAID BODY AND THROUGH A CONTROL CIRCUIT OPERATIVELY CONNECTED THERETO AND TO PROCESS CONTROL MEANS ADAPTED TO CONTROL THE HEAT FLOW BETWEEN SAID YARN AND ITS SURROUNDINGS RESPONSIVE TO CHANGES IN THE ELECTRICAL RESISTANCE OF SAID BODY; SAID YARN BEING OF ORGANIC THERMOPLASTIC MATERIAL; SAID BODY CHANGING ITS ELECTRICAL RESISTANCE WHEN ITS TEMPERATURE CHANGES BEING A SEMICONDUCTOR MADE OF A SINTERED MIXTURE OF METALLIC OXIDES; SAID SURFACE IN HEAT EXCHANGE RELATIONSHIP WITH SAID BODY HAVING THERMAL CONDUCTIVITY OF AT LEAST ABOUT 10-3 CALORIE/SEC. CM. *C., SAID BODY BEING ENCASED IN THE MATERIAL OF SAID SURFACE TO FORM A CAPSULE AROUND SAID BODY WIDTH NOT MORE THAN FIVE TIMES THE WIDTH OF SAID BODY AND NOT WIDER THAN ABOUT 1/4 INCH; SAID YARN BEING IN CONTINUOUS RUNNING CONTACT WITH AT LEAST ABOUT 1/5 OF THE SURFACE OF SAID CASPSULE; AND SUBSTANTIALLY ALL OF THE REMAINING SURFACE OF SAID CAPSULE, WHICH IS NOT IN CONTACT WITH THE RUNNING YARN, BEING SURROUNDED AND RIGIDLY SUPPORTED BY INSULATING MATERIAL HAVING THERMAL CONDUCTIVITY NOT MORE THAN HALF THAT OF THE MATERIAL IN WHICH SAID BODY IS ENCASED, AND NOT MORE THAN 10-3 CALORIE/SEC. CM. *C. 